Conventional bi-directional transceiver modules with 1550/1310 nm wavelength are utilized in a communication terminal system, such as the broad-band network and the optical fiber cable TV system. An optical transmitter converts an electric signal to an optical signal for transmission, whereas an optical receiver converts the received optical signal to an electric signal. The optical transmitter module connects the modulated light or signal emitted from the front section of a laser diode to an optical fiber. The light transmitted along the optical fiber is converted back to electrical signal at the other end of the optical receiver module.
In general, the optical transmitter and receiver are integrated in a single packaging arrangement module, so that the module is able to simultaneously transmit and receive light signal. Most packaging arrangements are typically assembled in a metal can in that the fabrication process is complicated and expensive. FIG. 1 of the attached drawings shows the structure of a conventional bi-directional transceiver using the “TO-can”. The bi-directional transceiver is fabricated with a metal packaging arrangement, including a TO-can laser diode 101, a TO-can signal detector 102, a thin film filter type wavelength division multiplexer 103, an optical fiber 104, and a metal housing case 107.
TO-can laser diode 101 includes a ball lens to convert an electric signal to an optical emitted signal for emission, whereas TO-can signal detector 102 receives an optical signal from the other end, and converts it to an electric signal. Thin film filter type wavelength division multiplexer (WDM) 103 can selectively reflects optical signals of a specific wavelength, by adjusting the reflection angle so that the optical signals are guided to the signal detector. Output optical signal 105 is emitted from TO-can laser diode 101 through thin film filter type wavelength division multiplexer 103, and enters optical fiber 104. Input optical signal 106 emitted from the other end is outputted from optical fiber 104, and reflected by thin film filter type wavelength division multiplexer 103 before entering TO-can signal detector 102. This type of packaging arrangement has many disadvantages. For example, it is an active alignment packaging method that is time-consuming, and the external quantum efficiency may be low due to the high light coupling loss between laser diode and optical fiber. In addition, because the TO-can is assembled with mechanical components, it has a larger size. Therefore, TO-can is suitable for low-speed transmission, but not for high-speed transmission.
FIG. 2 shows the basic structure of another type of transceiver, a planar light circuit, including a laser diode 201 for converting electric signals into optical signals, a signal detector 202 for converting optical signals into electric signals, a wave guide 203, and a substrate 204 for guiding optical signals to signal detector 202 and from laser diode 201 to an optical fiber. An optical transceiver is formed on a substrate to be used as a wavelength division multiplexer. However, as the structure uses only wave guide 203 for wavelength division, its ability in signal division is poor. In addition, as the coupling between laser diode 201 and wave guide 203 is difficult, both the optical loss and the fabrication cost are high.
To improve the poor signal division problem, a thin film filter 301 is added to wave guide 203, as shown in FIG. 3. The thin film filter is to separate the lights of different wavelengths to increase the isolation, and reduce the loss. But, as the coupling loss between laser diode 201 and wave guide 203 is too large, the overall loss of this improved structure is still high. In addition, the special thin film filter is expensive, and the overall fabrication process is complicated.
The silicon optical bench using silicon wafer as a basis and a semiconductor fabrication process is gaining popularity in high precision component production because the technology has the advantages of low material cost, mass productivity, ease of fabrication, and high precision. The function of a wavelength division multiplexer is achieved by installing a thin film filter on a silicon optical bench. Also, by combining optical lenses and silicon optical bench with thin film filters, the goal of high coupling efficiency can be achieved, and the external quantum efficiency can be improved.
However, the alignment design of a silicon optical bench affects the transmission path and the loss rate of the light. Therefore, the laser diode, signal detector, thin film, optical lens, and the locations and sizes of grooves must be accurately designed and produced in order to ensure the light to follow the designed path during reflection, refraction and penetration. During the transmission, the mode of the optical field changes after the light passing optical elements; hence, the optical loss occurs. The light coupling technique is important in reducing the loss. It is, therefore, important to utilize the optical characteristics of each optical element and a high precision production process to improve the mode of optical field, and achieve high coupling efficiency to avoid high loss.